Yes, I understand that.
I need the output to have blanks between the fields, which the REFORMAT doesn't allow, so the OUTFIL is the correct output format. What should I be specifying instead so that this works? Do I need to split this into 2 steps?

You either have not specified everything in your REFORMAT, or you have misspecified something in your OUTFIL BUILD. We can have no clue which, so I'll guess one way, and Sergeyken the other, so one of use will be correct :-)